I’ve had my SoundStage for a short spell now, and I like it. Comparing it to Propust isn’t wrong but kind of misses the point – not to say there is no overlap. It’s more than just a filtered mix, it makes you consider where your sounds sit in the mixing in a more dynamic way. You can also dial in exactly how filtered you want the effect to be, which is nice.
It is a different paradigm in mixing consideration in perhaps a similar fashion to Make Noise’s interest in decentralized mixing? It offers a different way of thinking about it in a nice compact package.
I will add that the stereo can be more complex than traditional patching as well. You can patch a sound into as many levels and panning orientations as you want. You can certainly think of it as “one voice to one patch point”, but I’ve enjoyed making sounds occupy different bands and panning positions. You could probably build a similar kind of thing with a bunch of Nearnesses and Proupsts, but I don’t think it would sound as nice as it wasn’t tuned to the purpose as SoundStage has been.
Which is to say: if you’re finding your work muddy, it should help. If you like the idea of what it does, it does what is says on the tin. It is also not the only way to accomplish this, but does so nicely in a very small foot print.